Such check valves are used in pneumatic systems if it is necessary to ensure that the pressure at a piece of pneumatic equipment, caused by the supply of fluid under pressure thereto, is to be maintained even if the feed pressure drops. The most usual field of application is equipment in which reciprocating motion is caused by actuator cylinders and in the case of which safety measures have to be taken to see that, if the supply of pressure fluid is interrupted, the actuator cylinder is locked and is not for instance lowered so that a hazard would occur. Lowering or the release of pressure from the actuator should in fact only take place if venting is caused to occur by the check valve by intentional operation thereof.
The check valve is attached by means of its attachment part to the component that is to be supplied with fluid as for instance a cylinder actuator, the outlet port arranged thereon being in communication with a drive space in the component. The connection part may selectively be connected, more especially via a 2-way valve, with a source of fluid under pressure or a means receiving the fluid, as for instance the atmosphere or a vacuum. -f the operating pressure is present at the connection part of the check valve the fluid will flow therethrough, since the pressure automatically moves the valve member against the thrust of the closing spring into the open setting so that the passage through the valve is opened up. -f the feed pressure falls under a certain threshold as dependent on the spring constant of the closing spring, the valve member will be moved into its shut setting and the pressure in the said drive space will be maintained. The intentional venting of this drive space may then later be caused by the operation of the operating device, this being done manually or by a drive fluid. The operating device will more particularly switch over the valve member by mechanical action out of its closing setting into the open setting and the path for the return flow will be free. Such controlled or override control valves are also termed releasable check valves.
A disadvantage with the check valves so far proposed of the above type is that the reduction in size of the attachment part by the designer is limited. This size is determined by the dimensions of the valve device, which is located in a recess in the attachment plate.
Accordingly one object of the invention is to provide a check valve of the initially mentioned, in the case of which the overall size or dimensions of the attachment part may be further reduced without then impairing the proper function of the valve.
A still further object of the invention is to make this possible without increasing the overall dimensions of the valve.